package main

// The retention as a preference (novox/hq issue 416, ADR 0262). The mesh writes the settings
// keep-daily, keep-weekly and keep-monthly into RetentionFile in this module's state, each defaulting
// to today's rotation, so a machine that sets none thins exactly as before. The controller does not
// type a setting yet (ADR 0164 is proposed), so this program is where a bad value is caught: it is
// refused here and never handed to restic (issue 346: a raw setting is an injection point).

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
)

// Retention is how many restore points each period keeps.
type Retention struct{ Daily, Weekly, Monthly int }

// TodaysRetention is the rotation before it was a preference (novox/hq ADR 0214), and still the
// manifest's default.
var TodaysRetention = Retention{14, 8, 6}

// RetentionFile is the file the mesh writes the retention into, in this module's state.
const RetentionFile = "retention.conf"

// A count from 1 to 9999 with no leading zero: 0 would make restic ignore the period, and a number
// past four digits is a typo, not a policy.
var count = regexp.MustCompile(`^[1-9][0-9]{0,3}$`)

// ParseRetention reads daily=, weekly= and monthly=, each once and each a count; anything else is
// refused naming the setting it came from.
func ParseRetention(text string) (Retention, error) {
	settingOf := map[string]string{"daily": "keep-daily", "weekly": "keep-weekly", "monthly": "keep-monthly"}
	seen := map[string]int{}
	for _, l := range strings.Split(text, "\n") {
		l = strings.TrimSpace(l)
		if l == "" || strings.HasPrefix(l, "#") {
			continue
		}
		k, v, ok := strings.Cut(l, "=")
		if !ok {
			return Retention{}, fmt.Errorf("%q is not key=value", l)
		}
		k, v = strings.TrimSpace(k), strings.TrimSpace(v)
		setting, known := settingOf[k]
		switch {
		case !known:
			return Retention{}, fmt.Errorf("%q is no retention this module reads (daily, weekly, monthly)", k)
		case seen[k] != 0:
			return Retention{}, fmt.Errorf("%s is given twice", k)
		case !count.MatchString(v):
			return Retention{}, fmt.Errorf("the %s setting is %q; it is a count from 1 to 9999", setting, v)
		}
		seen[k], _ = strconv.Atoi(v)
	}
	for _, k := range []string{"daily", "weekly", "monthly"} {
		if seen[k] == 0 {
			return Retention{}, fmt.Errorf("the %s setting is missing", settingOf[k])
		}
	}
	return Retention{seen["daily"], seen["weekly"], seen["monthly"]}, nil
}

// retention is this machine's: today's where the module was placed by a definition older than the
// file, else what the file says.
func (b *Backups) retention() (Retention, error) {
	path := filepath.Join(b.Where.State, RetentionFile)
	raw, err := os.ReadFile(path)
	if errors.Is(err, os.ErrNotExist) {
		return TodaysRetention, nil
	}
	if err != nil {
		return Retention{}, err
	}
	r, err := ParseRetention(string(raw))
	if err != nil {
		return Retention{}, fmt.Errorf("%s: %w", path, err)
	}
	return r, nil
}